package problem;

/**
* Title: 3. 数组中重复的数字
* Desc: 在一个长度为n的数组里的所有数字都在0到n-1的范围内。 
数组中某些数字是重复的，但不知道有几个数字是重复的。
也不知道每个数字重复几次。请找出数组中任意一个重复的数字。 
例如，如果输入长度为7的数组{2,3,1,0,2,5,3}，那么对应的输出是第一个重复的数字2。
* Created by Myth-PC on 26/01/2020 in VSCode
*/
public class P3DuplicateNumber {
    // Parameters:
    //    numbers:     an array of integers
    //    length:      the length of array numbers
    //    duplication: (Output) the duplicated number in the array number,length of duplication array is 1,so using duplication[0] = ? in implementation;
    //                  Here duplication like pointor in C/C++, duplication[0] equal *duplication in C/C++
    //    这里要特别注意~返回任意重复的一个，赋值duplication[0]
    // Return value:       true if the input is valid, and there are some duplications in the array number
    //                     otherwise false
    public boolean duplicate(int numbers[],int length,int [] duplication) {
        if (numbers == null || numbers.length < length || length <= 1) return false;

        for (int i = 0; i < length; i++) {
            if (numbers[i] != i) {
                if (numbers[numbers[i]] == numbers[i]) {
                    duplication[0] = numbers[i];
                    return true;
                } else {
                    // 注意此处
                    int temp = numbers[i];
                    numbers[i] = numbers[numbers[i]];
                    numbers[temp] = temp;
                }
            }         
        }

        return false;
    }
    public static void main(String[] args) {
        P3DuplicateNumber p3 = new P3DuplicateNumber();
        int[] numbers = {2,1,3,1,4};
        int[] duplication = {-1};
        System.out.println(p3.duplicate(numbers, 5, duplication));
        System.out.println(duplication[0]);
    }
}